The present disclosure relates to a reverse battery protection device and an operating method thereof, and particularly, to a reverse battery protection device in which a low voltage DC/DC converter is normally operable in a low voltage, and an operating method thereof.
Typically, an electric vehicle or a hybrid vehicle includes a high voltage battery providing a high voltage to a driving motor and a low voltage battery providing a low voltage to electronic devices.
In battery charging of the electric vehicle or the hybrid vehicle, the high voltage battery is charged through an external power source or a generator inside the vehicle and the low voltage battery is charged by converting the high voltage of the high voltage battery into the low voltage.
A device converting the high voltage into the low voltage is the low voltage DC/DC converter (hereinafter referred to as “LDC”), which converts the high voltage from the high voltage battery into the low voltage and charges the low voltage battery or delivers power to a load device.
On the other hand, the electronic devices are connected to a reverse battery protection device in order to protect the battery and a system from damages according to reverse connection of the battery.
Here, the reverse connection of the battery means that the battery is reversely, not normally, connected to a circuit.
For example, for an LDC connected to a battery and an electronic system, a reverse battery protection device is necessary for simultaneously performing a battery charging operation and a reverse connection preventing operation. Typically, a metal oxide silicon field effect transistor (MOSFET) is used as a switching device.
In detail, a reverse battery protection device using the MOSFET as the switching device may prevent reverse connection of the battery through a diode inside the MOSFET and charge the battery by allowing a channel current to flow between a source and a drain of the MOSFET
A typical reverse battery protection device using a MOSFET as a switching device is described with reference to FIGS. 1 and 2.
Referring to FIG. 1, FIG. 1 illustrates a reverse battery protection device using a p-channel MOSFET.
In a circuit illustrated in FIG. 1, when a battery is normally connected to the circuit, a current flowing through a diode inside the MOSFET charges an output capacitor of an LDC.
When the output capacitor of the LDC is charged, a current flows through the LDC and accordingly the current flows the reverse battery protection device. Then a voltage is applied to a gate of the MOSFET.
According to the application of the voltage to the gate of the MOSFET, a p-channel is formed, a current flows through the formed p-channel, and the current flowing through the diode charges the battery while flowing through the channel of the MOSFET.
On the contrary, when the battery is reversely connected, a current does not flow through the diode inside the MOSFET and the output capacitor of the LDC is not charged. Then the voltage is not applied to the gate of the MOSFET and the current does not flow.
FIG. 2 illustrates a reverse battery protecting device using an N-channel MOSFET.
In a circuit illustrated in FIG. 2, when a battery is normally connected to a circuit, a current flowing through a diode inside the MOSFET charges an output capacitor of an LDC.
When the output capacitor of the LDC is charged, a current flows through the LDC and accordingly the current flows through the reverse battery protecting device. Then a voltage is applied to a gate of the MOSFET.
When the voltage is applied to the gate of the MOSFET, the N-channel is applied, and a current flows through the formed channel, a current flowing through the diode flows through the channel of the MOSFET and charges the battery.
On the contrary, when the battery is reversely connected, a current does not flow through the diode inside the MOSFET and the output capacitor of the LDC is not charged. Then a voltage is not applied to the gate of the MOSFET and the current does not flow.
In this way, since different in kind of MOSFET but same in basic operations, the reverse battery protection devices in FIGS. 1 and 2 prevent reverse connection of the battery and charge the battery.
As described above, the related art using a MOSFET as a switching device uses a scheme that a current flows through a power supply circuit and a voltage of the battery is applied to a gate of the MOSFET.
Accordingly, a gate voltage of the MOSFET is determined by a voltage of a connected battery and the gate voltage of the MOSFET is affected by a voltage variation of the battery.
When the connected battery is fully charged, a normal voltage is applied to the gate of the MOSFET. When the voltage of the battery is lowered by battery discharge or a cold crank phenomenon due to a low temperature, the gate voltage of the MOSFET is also lowered.
When the gate voltage of the MOSFET is lowered, the MOSFET does not operate in a normal operation range, and a magnitude of resistance (Rds) between a drain and a source of the MOSFET becomes large and a loss of a current flowing through the MOSFET also becomes large.
In addition, when the battery voltage becomes lowered, a current does not normally flow the reverse battery protection device and the reverse battery protection device operates unstably.